Process and Related Equipment for Burning Industrial Plant Waste

ABSTRACT

The present invention is directed to a process for burning industrial plant waste, equipment for burning such waste, and a steam-generating boiler that uses the calorific power of the waste for generating energy without polluting the atmosphere. The present process is carried out by controlling the viscosity of the waste, thus burning same out, and the generated steam is advantageously used for the generation of energy through a generator.

CROSS-REFERENCE TO RELATED APPLICATION

This application is entitled to priority based on Brazilian Patent Application Serial No. PI 0900363-0, filed on Feb. 2, 2009, the contents of which are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention is related to the use of industrial plant waste as fuel.

SUMMARY OF THE INVENTION

In a first aspect, the invention is directed to a process for burning industrial plant waste in order to use the calorific power thereof, such waste having never been used for this purpose to date. In another aspect, the invention is directed to equipment for burning industrial plant waste as fuel, typically in a steam-generating boiler.

The following text refers to soy molasses and bagasse without, however excluding any other waste having similar characteristics that may contain any type of sugar (e.g., sugar cane), or substance (e.g., starch) that may be hydrolized into sugars; for example, maize, beet, potato, castor, canola, sesame, peanut, palm, cotton, orange peel, sunflower, etc., known by one skilled in the art and for which eventual adaptations for the accomplishment of the invention are made without the need of empirical tests.

As used herein, “molasses” means a sugar waste that is separated, for example, by distilling the liquid solvent used to wash the bran resulting from the crushing of a plant (grain, seed, peels, and the like).

As is well known, to obtain soy oil, soy grains are pressed or extracted, and then the oil is separated from the solid cake. The cake, in turn, is submitted to a thermal treatment, dried, cooled and stored to be marketed in the future. This process produces a soy bran that may contain from 44 to 50% protein (a 12.5% humidity) depending on the separation.

The process for providing a protein-rich concentrate is an additional extraction stage. The above-mentioned bran is submitted to extraction by using a water-alcohol mix, thus providing the protein-rich concentrate (65 to 74% protein on a dry base) and micelles. The concentrate is pressed through a thermal treatment, dried, cooled and finally stored. It is used mainly for manufacturing animal rations. The micelles, that is, a mixture of sugars, water and alcohol, proceed to the distillation stage, and then first of all the alcohol is separated from the remaining liquid that is returned to the process. It is then concentrated to remove most of the water, thus obtaining the molasses (30%-80% solids).

The soy molasses contains a high content of sugars that may be transformed into alcohol and so it may be submitted to fermentation. The waste of the fermentation is known as bagasse. This bagasse mainly contains sugar waste, minute bran grains that are too small to be caught by any filter, plus lipid waste and ash. Also, the sugar cane molasses may contain sugars that may be easily transformed into alcohol to be submitted to the traditional fermentation. Both the bagasse generated in the process for producing alcohol from sugar cane and the sugar cane molasses may be concentrated to be used as plant fuel, e.g., soy molasses and bagasse.

The application of soy molasses as an additive to animal rations is known. However, most of said molasses is a waste that has been considered an undesirable by-product so far in view of the difficulty to market same and the lack of storage room.

Burning the molasses would be an option to discard same. However, in conventional devices it is not possible to burn same without making a number of changes to allow burning the molasses for a longer period, thus making it possible to identify the problems. A number of problems have arisen, preventing the waste from being burned for more than 2 hours: for example, the molasses could not be heated to be atomized onto the burner, thus not attaining any control of temperature, concentration and viscosity, and such parameters are of the utmost importance for the atomization and consequent control of the combustion. Such difficulties prevented the molasses from being conveyed into the burner, thus tests could not be conducted for determining the optimum concentration, temperature and viscosity to provide a complete combustion.

In the BPF oil (heavy/residual fuel oil) burning process it is not required to control the viscosity and concentration, since such parameters are guaranteed by the fuel supplier. There is no difficulty in the heating, since conventional heat exchangers heat the oil without the occurrence of scale-forming and crystallization in the sugar.

In the case of some wastes, such as the molasses, this does not occur, since the sugar is burned when it reaches more than approximately 60 degrees centigrade, thus crystallizing and consequently turning into coal, and the coal forms scale in the inner piping of the exchanger, thus wasting the fuel and preventing the burning. With temperatures below 60 degrees centigrade, the combustion is incomplete, since it is not possible to either heat the molasses as required or keep the viscosity in a range between 50 and 70 centistokes. This value was found after a number of tests and O₂, CO₂ and CO measurements have been made.

The solution found was to inject steam directly into the molasses at a high speed by using injectors, and heating same to about 100 degrees centigrade without any problem, and then a viscometer carries out the real time measurement of the viscosity and sends a signal to open or close a steam control valve in the injector, according to the set point used. The molasses proceeds to a pressure tank and is sent to the burner directly. Such controls make it possible to develop the present burning process with optimum temperature, viscosity and concentration of the molasses.

Another problem found due to the burning of the molasses is the generation of a highly soluble hygroscopic white ash. Said ash impregnates all the thermal exchange areas of the boiler as well as ducts, exhaust fans (furnace, evaporator, super-heater). Said ash accumulates in the exchange areas, and after two hours the temperature of the gases at the furnace outlet reaches 550° C., but should never be higher than 420° C. It also accumulates in areas where no thermal exchange takes place, such as: boiler output ducts, pre-air, savers, multi-cyclone, exhaust fans. Such accumulation increases as time goes by and there is loss of load in the whole equipment, consuming the exhaust fan and preventing the burning thereof for more than one week.

The solution found for the ash impregnation in thermal exchange areas (furnace, evaporator, super-heater) was the installation of soot blowers. In each area, a model that would have the best output was used. Two blowing pressures were tested: 12 and 21 Kgf/cm². It was found that the gas temperature at the furnace with a 12 Kgf/cm² pressure falls to 440° C., and to 390° C. with a 21 Kgf/cm² pressure.

In areas where there is no thermal exchange, such as: boiler exit ducts, pre-air, savers, multi-cyclone, caps provided with threads and rotating valves have been provided, thus removing the ashes directly to a dump-cart.

After the adjustments of such parameters a good result was attained.

Another characteristic of the molasses is that many pollutants are emitted when it is burned, causing damages to the environment. Besides, it may only be burned in blast furnaces, at a temperature of about 1,300 degrees centigrade, an expensive procedure that does not bring about any advantage in the cycle of exploitation of plant material.

It was noticed that the burning process caused another problem, that is, the emission of smoke containing particulates above 5.000 mg/m³ gas, sending out a fine white dust (ashes) directly to atmosphere, thus exceeding the legal limits.

Differently from other biomass fuels, most part of the ashes of which is insoluble, the molasses ash is soluble, so the solution used to prevent the emission thereof into the environment has to be different.

A first attempt to reduce this emission of particulates was the use of a multi-cyclone and a gas-washing unit provided with water sprinklers. However, when a new burning of the molasses would be carried out, it was noticed that the multi-cyclone and the gas-washing unit could reduce the particulates in the gas from 5,000 mg/Nm³ to 2,500 mg/Nm³, but did not reach the 400 mg/Nm³ required by the IAP (Instituto Ambiental do Paraná—an environmental regulatory institution in the Brazilian State of Paraná). It was also noticed that the white ash obliterated the multi-cyclone as time went by, and the only way to continue was to stop the washing process every 3 days, that is, by discontinuing the process, thus making the design impracticable.

Continuing the burning process, it was found that this occurred because the gas-washing equipment which is very common in the alcohol and sugar industry only removes the water-insoluble particulates contained in the gases, so soluble particulates would go through the washing unit without being removed.

The option adopted was to remove the multi-cyclone and change the washing unit. Then, a venturi washing unit was used to provide a highly efficient gas-liquid mixture to promote the collection of both soluble solids and insoluble solids, followed by a cyclonic separator, a droplet separator and a mist separator, both installed on top of the cyclonic separator. A saturation boom was installed before the venturi for the purpose of promoting the saturation of the gases in the boiler before they entered into the venturi, the soluble and insoluble solids would be caught in the latter, and the gas would leave the saturated washing unit together with water containing soluble and insoluble solids. The excess water would be separated by the cyclonic separator, droplets bigger than 25 microns would be removed by the first droplet separator, and droplets (mist) bigger than 3 microns would then be separated by the mist separator (demister), drawing the soluble particulates along, and launching the molasses burning gases with a concentration lower than the one required by the IAP into the environment.

When searching for alternative uses for molasses and/or bagasse, in particular from soy, it was surprisingly found that this waste can be burnt as fuel. Particularly, the soy molasses and/or bagasse may be used as fuel in steam-generating boilers, for replacing fossils fuels such as BPF oil or any other usually used for that purpose, with the advantages of preventing the accumulation of a by-product that has been considered a useless polluting waste so far, advantageously using the calorific power thereof, thus saving money by replacing nobler and more expensive fuels.

In a first aspect the present invention is directed to a process for burning molasses and/or bagasse, characterized by the following stages:

concentrating molasses, bagasse or mixtures thereof, until a solid content of between 30 and 85% is attained;

preheating between 60 and 100° C., until a suitable viscosity to its complete burning is attained in the burner;

burning in a flame burner, through nebulization.

In particular, but without excluding any other condition, the following aspects are applied advantageously:

the molasses, bagasse or mixtures thereof are from soy or sugar cane;

the solid content of the molasses, bagasse or mixtures thereof is between 60 and 80%;

the pre-heating is carried out through direct steam injection;

-   -   the pre-heating is carried out to about 100° C.; and,     -   the viscosity of heated molasses and/or bagasse is between 30         and 80 cst (centistokes).

The burner is of the same type usually used for BPF oil and gas, for example, Saacke SSB-S200 serie E-609 E-610 Burner.

It was found that the complete combustion of molasses and/or bagasse is favored in the above cited viscosity ranges, with expected variations as a function of the plant origin of this new fuel. It was also found that the calorific power provided is higher than the one of the solid fuel burning as chips.

In another aspect of the invention, equipment for burning molasses is also contemplated, which equipment comprises:

a vessel for containing molasses and/or bagasse;

a pump for pumping the molasses and/or bagasse into a direct steam injecting device;

a device for injecting steam directly into the molasses and/or bagasse;

a device for checking and controlling the viscosity, associated to the direct steam injecting device;

a pump for pumping the molasses and/or bagasse into a burner; and

a nebulized liquid fuel burner.

The equipment of the invention functions as follows: the molasses and/or bagasse, with a solid content between 30 and 85%, are placed in a vessel wherein they are heated by injection of direct steam—the steam injecting device may be independent or a device incorporated into the vessel. The viscosity of the molasses and/or bagasse is higher than the one suitable to the complete burning, thus the steam is injected until the viscosity lowers to the suitable range, typically between 40 and 80 cst, and then the liquid is pumped into the burner. The equipment of the invention comprises a device for checking and controlling the viscosity, for example, a viscometer and a set of pipes and valves that can return the pumped liquid to the vessel in the event the viscosity is higher or lower, as well as a specific activator able to act on the direct steam injector in the mass of molasses and/or bagasse, thus increasing or decreasing the amount of steam in order to increase or decrease the viscosity, as required. Devices for checking and controlling the viscosity for this purpose are known by one skilled in the art, so specific details on same are not an essential aspect of the invention.

The liquid fuel burning device of the equipment of the invention is known in the state of the art, associated with an air compressor to allow for the nebulization of the fuel. Advantageously, said device also can burn gaseous fuel concomitantly, such as GLP (liquefied petroleum), when it is desired to supplement the burning of molasses and/or bagasse.

The equipment of the invention is typically associated with a steam-generating boiler. In this configuration, such boiler may be a multi-fuel boiler, or may contain several molasses and/or bagasse burners, soot blowers, etc. Said boiler may be provided with a variety of additional devices, such as a system for controlling the emission of solid particles, according to the legal requirements of the region where the process is carried out.

Advantageously, the steam generated in the boiler is sent to an energy generating turbine that can be advantageously used in the production process that generated the plant waste, thus making the manufacturing system self-sufficient.

Preferably, the equipment also comprises soot blowers that make it possible to clean the interior of the boiler, for example, once an hour, not requiring stops for the cleaning, thus improving the combustion.

Suitably, without excluding any other system, said system for controlling the solid particle emission comprises at least a venturi inside which the burning gases and water are intimately contacted, and a cyclonic separator, a droplet separator and a mist separator where the mist is sent to after leaving the venturi.

Instead of using a venturi, a washing unit with absorption columns or water pump can be used.

A merely illustrative example of an embodiment of the invention is given below, without posing any restriction to its scope, or of the attached claims. The figure is schematic, the dimensions or proportions of which do not correspond to the reality, since its purpose is only to clarify an embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is schematic overview of equipment for burning industrial plant waste, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The FIGURE attached hereto illustrates schematically a facility where soy molasses is burned to generate steam in a boiler (1), extracted in a turbine (2) for the 12 Kgf/cm² steam and the 1.5 Kgf/cm² leak steam; and finally electricity is generated (4) through a generator (3). The micelles from the extraction of sugars (not illustrated) get into a four-stage device that is called molasses concentrator (8) which sends the molasses to a pressure tank (10). With the aid of the steam the micelles are concentrated to 80 brix before being sent to the pressure tank (10). The amount of steam injected in the concentrator (8) is controlled by a brix measuring device (9), at the outlet of the concentrator (8), that opens or closes a steam valve (7) according to the desired concentration. The molasses is concentrated at 80 brix and then sent to a pressure tank (10). The molasses is concentrated to remove the water, since the dry substance (Carbon, Hydrogen, Sulfur and Nitrogen) is of interest. The molasses is sent to small tanks (19) and (20) and the injectors (13) and (14) through pumps (11) and (12), where it is heated by injecting direct steam. The injected amount of steam is controlled by control valves (15) and (16) that receive the signal from viscosity measuring devices (17) and (18), respectively. If the viscosity is too high, the measuring devices (17) and (18) send a signal to open said valves, and if it is too low they send a signal to close same, depending on the set point chosen. The pumps (21) and (22) pump the molasses into the burners (Q2) e (Q1) with adjusted concentration, pressure, temperature and viscosity.

In this particular example, the steam generated by the boiler (1) has a pressure of 42 kgf/cm² and leaves through a pipe towards a turbine (2), where the 12 kgf/cm² extraction steam and 1.5 kgf/cm² leak steam are extracted. It is this decrease of the steam pressure that makes it possible to generate electric energy (3). So, two lines with the 12 kgf/cm² extraction steam (5) and the 1.5 kgf/cm² leak steam (6) are directed to the molasses generating plant.

The boiler (1) also can generate steam with other fuels, since it is provided with a grid (23) for supporting solid fuel, such as soy chips or crust.

Burners (Q1) e (Q2) are further provided with booms that are able to burn gas.

The boiler (1) is further provided with a soot blower (not illustrated) that it is a rotating steam injector, for the purpose of removing eventual scale inside the boiler.

The gases resulting from the burning of the molasses in the boiler (1) proceed to a particulate control system.

Said particulate control system is comprised of a saturation boom (24), a venturi washing unit (25), a cyclonic separator (26), a droplet separator (27) and a mist separator (28).

When the burning steams leave the boiler (1) through the saturation boom (24) they receive an amount of water that allows for the saturation thereof. After the saturation, they get into the venturi washing unit (25), where whole particulates are collected and washed by injecting water into the venturi (25). The gases get into the lower part of a cyclonic separator (26), where the centrifugal force separates the amount of injected water present in said gases. The water carries insoluble solids and a portion of soluble solids along. The gases still continue carrying the drops that solubilized the soluble solids and that appear as particulates at the outlet of chimney (30), if the measurement is carried out. Still inside the body of the cyclonic separator (26), the gases pass through a droplet separator (27) that catches droplets bigger than 25 microns, proceeding to another mist separator (28) that catch droplets bigger than 3 microns. Thus, the gases that leave the cyclonic separator (26) are within the limits accepted by the environmental agency.

One skilled in the art, with the aid of the teachings given herein, as well as the example and the accompanying figure, will understand the invention and be able to carry out in an equivalent way, not expressly described, but within the functions and the results as learned herein, and protected in the attached claims. 

1. A process for burning industrial plant waste, the process comprising: concentrating molasses, bagasse or mixtures thereof, until a solid content of between approximately 30% and approximately 85% is attained; preheating the concentrated molasses, bagasse or mixtures thereof between approximately 60° C. and approximately 100° C., until a viscosity suitable for complete burning is attained; burning the preheated, concentrated molasses, bagasse or mixtures thereof in a flame burner, through nebulization.
 2. The process according to claim 1, wherein the molasses, bagasse or mixtures thereof are from soy, sugar cane, or other wastes that contain sugar or substances that may transformed into sugar through chemical or enzymatic hydrolysis.
 3. The process according to claim 1, wherein the solid content of the molasses, bagasse or mixtures thereof is between approximately 30% and approximately 80%.
 4. The process according to claim 1, wherein the pre-heating is carried out through direct steam injection into the molasses, bagasse or mixtures thereof through an injector.
 5. The process according to claim 1, wherein the preheating is carried out to about 100° C.
 6. The process according to claim 1, wherein the viscosity of the molasses, bagasse or mixtures thereof is between approximately 30 centistokes and approximately 80 centistokes.
 7. The process according to claim 1, wherein the burner is also adapted to burn BPF oil and gas.
 8. Equipment for burning industrial plant waste, the equipment comprising: a pressure tank for initially storing molasses, bagasse or mixtures thereof; two intermediate tanks connected to the pressure tank for storing the molasses, bagasse or mixtures thereof at a suitable viscosity for burning; two burners of nebulized liquid fuel connected to the two intermediate tanks for burning the molasses, bagasse or mixtures thereof; two direct steam injecting devices for injecting steam into the molasses, bagasse or mixtures thereof being sent to the two intermediate tanks from the pressure tank; two viscosity or temperature measuring devices for measuring the viscosity or temperature of the molasses, bagasse or mixtures thereof being sent to the two intermediate tanks from the pressure tank; two first pumps for pumping the molasses, bagasse or mixtures thereof from the pressure tank to the two intermediate tanks through the two direct steam injecting devices and the two viscosity or temperature measuring devices; two control valves for controlling the amount of steam injected in the molasses or bagasse by the two direct steam injecting devices based on the two viscosity or temperature measuring devices; and two pumps for pumping the molasses, bagasse or mixtures thereof into the two burners from the two intermediate tanks.
 9. The equipment according to claim 8, wherein the two burners are adapted to burn gaseous fuel concomitantly.
 10. The equipment according to claim 9, further comprising a steam-generating boiler in which the molasses, bagasse or mixtures thereof is burned.
 11. The equipment according to claim 10, wherein the boiler is adapted to burn solid fuel including soy chips or crusts.
 12. The equipment according to claim 10, further comprising soot blowers for the boiler.
 13. The equipment according to claim 10, further comprising a system for controlling the emission of solid particles from the boiler, including soluble and insoluble material, the system including: a venturi washing unit; a cyclonic separator; and a mist separator.
 14. The equipment according to claim 10, further comprising a system for controlling the emission of solid particles from the boiler, the system including: a washing unit; a cyclonic separator; and a mist separator.
 15. The equipment according to claim 14, wherein the washing unit includes at least one of absorption columns and bubbling columns. 